This invention relates to the art of fire resistant insulated electrical wire and/or cable constructions and more particularly to an improved insulated wire and/or cable construction that will function normally while subjected to heat and temperatures up to 1750.degree. F. for a period of one hour.
There is a need for insulated electrical wire and/or cable constructions capable of withstanding the sustained high temperatures of fires to 1750.degree. F. that may originate either externally of the wire or cable or internally as a result of electrical short circuit conditions.
Ceramics and/or glass fibers have been used heretofore to prepare electrical cables. In addition, coated fabrics and ceramic structures have been prepared with a combination of glass fiber fabrics and metal oxides.
U.S. Pat. No. 2,587,916 of Squier discloses a heat-detecting cable of a pair of electrical wires separated by a glass composition containing barium oxide and/or boron oxide which is non-conductive at normal temperature but is conductive at high temperatures. In one embodiment, the glass is in the form of a fabric having finely divided refractory materials distributed therein to enhance the ability to withstand high temperature. The barium oxide and/or boron oxide containing fiberglass tape does not insulate the wires at high temperature but rather provides a conductive path so as to detect high temperatures.
U.S. Pat. No. 3,602,636 of Evans discloses an electrical cable where the conductors are helically wrapped with an open weave glass cloth having a coating of a flame resistant synthetic rubber together with an extruded sheath of polyvinylchloride (PVC) or the like covering the assembled cable.
U.S. Pat. No. 3,632,412 of Blance et al. discloses a pressure sensitive adhesive for a Class F (high temperature service) electrical tape. The adhesive is an interpolymer of acrylates, methacrylates and hydroxyacrylates or hydroxymethacrylates. Glass cloth is included among the useful backing members for this tape.
U.S. Pat. No. 3,013,902 of Bugosh discloses fabrics coated with colloidal alumina and a final coating of a polymer having a plurality of free carboxylic acid groups. Glass fibers are included in the list of materials which may comprise the fabric substrate. These textile products have improved resistance to soiling and improved washability. No use for the fabrics in electrical tape, wire or cable is disclosed or suggested.
U.S. Pat. No. 3,095,336 of Church et al. discloses the preparation of ceramic articles laminated with glass fabric by impregnating glass fibers with a mixture of a thermosetting resin and a ceramic filler, curing the resin, heating to gasify the resin and then heating to an elevated temperature to fuse the glass fabric and the ceramic filler to produce rigid, laminated ceramic structures having high strength characteristics. No use in electrical tape, wire or cable is disclosed or suggested.
Plastic compounds (principally vinyl) and various elastomeric compounds are widely used as insulation and protective jacketing for electrical wire and cable products. When exposed to fire at an ignition flame temperature of 700.degree. F. or above, vinyl and virtually all other elastomers provide fuel to propagate the fire and burn emitting toxic smoke.
The danger associated with electrical fires involving wire and cable insulation and jacketing have been recognized by the industry and a variety of efforts have been made to improve the performance of these products. Thus, fire retardant electrical insulation has been formed of asbestos fiber which has been widely used as part of the insulation and cover wrap material in the construction of fire resistant electrical wire and cable. However, asbestos fibers have now been identified as a carcinogen, and attempts are being made to phase out the use of asbestos.
In an effort to meet improved smoke and fire resistant standards for electrical wire or cable in high performance applications such as marine (ship and submarine), mining installations, oil drilling derricks, nuclear power plants, etc., explosion-proof, fire resistant conduit installations are normally specified. This involves the installation of steel pipe into which the electrical wires or cables are placed. A fire resistant compound is forced through the pipe under pressure to insulate the vinyl coated wires or cables from the effects of fire. This type of installation does limit the self propagating effects and smoke development of electrical fires. It is, however, costly and though minimizing flame transfer externally of the steel conduit acts to confine heat within the conduit, burning the wire or cable, creating an electrical short circuit condition and subsequent loss of power.